The long-term goal of this research is a better understanding of the processes which cause bone resorption and accretion in vivo. Current objectives include: (a) To investigate the mechanisms by which parathyroid hormone increases blood calcium levels during long-term infusion of physiological doses of the hormone. (b) To study the effect of calcitonin on acid-base balance, skeletal metabolism and plasma ionic calcium. (c) To clarify the role of the central nervous system in calcium homeostasis. (d) To investigate the role of prostaglandins in bone resorption.